1. Field of the Invention
This invention relates to image display apparatuses, and, in particular, relates to an image display apparatus equipped with an input terminal section for inputting at least two kinds of image signals having different horizontal scanning frequencies to each other.
2. Description of the Related Arts
Recently, with the variety of image signals, there appears not only video signals of the conventional NTSC system but also the video signals different from those of the NTSC system such as video signals of the second generation of the EDTV (Enhanced Definition TV) and High Definition TV (HDTV) systems.
The horizontal scanning frequency of the NTSC system is 15.75 kHz and the horizontal scanning frequency fully decoded form in the second generation EDTV is 31.5 kHz and the horizontal scanning frequency of the HDTV is 33.75 kHz. The video signal of the NTSC system is referred to as a single-density signal and the video signals such as those of the second generation EDTV and the HDTV are referred to as a double-density signal hereinafter.
FIG. 1 is a block diagram of a conventional image display apparatus for monitoring input signals, which is capable of displaying both the single-density signal and the double-density signal in the prior art.
In FIG. 1, the numeral 1 denotes an input terminal section (referred to as a single-density terminal section) for inputting the single-density signal composed of three input terminal systems 1a, 1b, 1c. Each of the three input terminal systems 1a, 1b, 1c includes an S-terminal for inputting an S-video signal having a luminance signal and a color signal separated from each other as mentioned hereinafter, a terminal for inputting a composite video signal Cv and a pair of terminals for inputting L (light) and R (right) sound signals.
The numeral 2 denotes a double-density terminal section composed of three input terminal systems 2a, 2b, 2c. Each of the three input terminal systems 2a, 2b, 2c includes a terminal for inputting a luminance signal Y, a terminal for inputting color difference signals Pb, Pr as mentioned hereinafter and a pair of terminals for inputting L (light) and R (right) sound signals.
A plurality of single-density signals inputted to the single-density terminal section 1 through the three input terminal systems 1a, 1b, 1c are inputted to a switch 3, and one of them is selectively inputted to a single-density signal processing circuit 5.
A plurality of double-density signals inputted to the double-density terminal section 2 through the three input terminal systems 2a, 2b, 2c are inputted to a switch 4, and one of them is selectively inputted to a double-density signal processing circuit 6.
When both output signals from the single-density and double-density signal processing circuits 5, 6 are inputted to a switch 7, one of them is selectively outputted therefrom and is inputted to a well known output circuit 8 for displaying an image on a CRT 9. After undergoing various kinds of video signal processings and being amplified by the output circuit 8, the output signal therefrom is inputted to the CRT 9 to display an image thereon. Incidentally, the description of the sound signal processing section is omitted here.
Next, a description is given of the single-density terminal section 1 and the double-density terminal section 2 referring to FIG. 2.
FIG. 2 is a front view showing a terminal section of the image display apparatus of the prior art.
In FIG. 2, the single-density input terminal section 1 includes the three input terminal systems 1a, 1b, 1c, each having the S-terminal (video S), the terminal (video Cv) for inputting the composite video signal Cv and the pair of terminals (sound L, R) for inputting the R, L sound signals.
The double-density input terminal section 2 includes the three input terminal systems 2a, 2b, 2c, each having the terminal (Y) for inputting the luminance signal Y, the terminals (Pb), (Pr) for inputting the color difference signals Pb, Pr, and the pair of terminals (sound L, R) for inputting the sound signals R, L.
In the conventional image display apparatus having both the single-density input terminal section 1 and the double-density input terminal section 2, it is necessary to connect a cable to either the single-density input section 1 or the double-density input terminal section 2 knowing that the signal intended to be inputted is the single-density signal or the double-density signal.
When the cable for the single-density signal is erroneously connected to the double-density input terminal section 2 or when the cable for the double-density signal is erroneously connected to the single-density input terminal section 1, a correct image can not be displayed on the CRT 9. In most cases, pin-plugs based on the RCA standards are employed in all the input terminals for inputting the composite video signals Cv, L, R sound signals, the luminance signal Y, and the color different signals Pb, Pr. Thus, such cable is possible to be connected to either the single-density input terminal section 1 or and the double-density input terminal section 2, resulting in an erroneous connection to a wrong input terminal section.
Further, there are problems of a space and a production cost because it requires two separated input terminal sections 1 and 2.